The present invention relates to a fuel supply for a fuel cell. More particularly, the invention provides a fuel supply configured to maintain a lowered backpressure across a fuel outlet.
Fuel cells in general, and hydrogen fuel cells in particular, have received increased interest as possible power supplies for portable electronic devices. A fuel cell is an electrochemical device for continuously converting chemicals into direct-current electricity. A fuel cell typically includes an anode and a cathode separated by an ionic-conducting electrolyte, and also any necessary systems for moving fuel into the cell or waste out of the cell. Fuel is continuously fed to one of the electrodes, and a reactant is fed to the other electrode. Electrons participating in the reaction flow from one electrode to the other via an external circuit, thus powering an attached device.
In a hydrogen fuel cell, hydrogen gas is fed to the anode, and oxygen is fed to the cathode. At the anode, the hydrogen gas is oxidized to H+ ions. The hydrogen ions travel through the electrolyte to the cathode, while electrons from the oxidation reaction travel through an external circuit to the cathode. At the cathode, the electrons reduce oxygen atoms, which then react with the hydrogen ions to form water as a waste product.
Fuel cells in general, and hydrogen fuel cells in particular, offer several advantages over traditional batteries. First, unlike batteries, a fuel cell produces electricity from fuels that are fed to the fuel cell only as needed. Therefore, the life of the fuel cell is theoretically unlimited, requiring only that the fuel supply be periodically replenished or replaced. This allows a fuel cell to be installed as a permanent part of a portable device, with provision for a refillable or replaceable fuel supply. Second, because hydrogen fuel cells produce water as a waste product, the use of fuel cells presents fewer environmental concerns than batteries, which generally contain hazardous chemicals such as heavy metals or acids. Third, the output voltage of fuel cells remains generally constant throughout the life of the fuel cell, as opposed to a battery, which may suffer from reduced output voltage over the course of the battery lifetime.
A fuel cell may use a fuel in any form, solid, liquid or gas. For example, either compressed hydrogen gas or cryogenic liquid hydrogen could be used to power a hydrogen fuel cell. However, these sources may be expensive and dangerous to use. A more convenient source of fuel for a hydrogen fuel cell may be a chemical (or a solution of a chemical) with easily oxidizable protons, such as methanol, or one that releases hydrogen gas in the presence of a catalyst, such as a borohydride solution. Because these fuels are relatively safe and easy to use and to store at room temperature, they may be used in disposable or rechargeable fuel supplies.
While methanol or borohydride (or similar) fuel supplies may be convenient to use, they may also pose some problems. For example, the expansion of gases inside the fuel supply caused by changes in atmospheric pressure may force fuel through the interface at which the fuel supply couples to the fuel cell. This leakage may contaminate the electronics in the portable device, possibly causing device failure, or may leak out of the device and pose a safety concern.
The present invention provides a fuel supply for a fuel cell. The fuel supply includes a fuel storage area, a fuel outlet configured to pass fuel from the fuel storage area, and a backpressure regulator configured to maintain a lowered pressure within the fuel storage area relative to atmospheric pressure outside of the fuel storage area when fuel is not being transferred to the fuel cell.